Labyrinth seal

Abstract

A labyrinth seal suppresses leakage of fluid through a gap between a circumferential outer surface of a rotating body, having an axis of rotation, and a circumferential inner surface of a stationary body provided on an outer side of the rotating body, by increasing fluid energy loss caused by vortices. Said leakage occurs in an axial direction from a high pressure to a low pressure side. A step is formed on the outer surface such that the diameter of the low pressure side is smaller than that of the high pressure side. A fin extending radially inward from the inner surface is formed on at least the low pressure side of the step. An annular groove is formed to extend in a circumferential direction in the outer surface, in at least one portion of the area axially between the step and the fin.

The invention claimed is: 
     
       1. A labyrinth seal comprising:
 a rotating body rotatable about an axis of rotation and having an outer circumferential surface; 
 a stationary body provided radially outward of the rotating body and having an inner circumferential surface; 
 a gap being formed between the inner circumferential surface and the outer circumferential surface; 
 wherein the labyrinth seal is configured to inhibit leakage of fluid passing axially from a high-pressure side to a low-pressure side through the gap, 
 wherein the labyrinth seal further comprising: 
 a step formed on the outer circumferential surface of the rotating body such that the rotating body has a large diameter portion on the high-pressure side and a small diameter portion on the low-pressure side so that an annular surface viewing from a point on the rotation axis is formed at a boundary between the large diameter portion and the small diameter portion, 
 a fin extending radially inward from the inner circumferential surface of the stationary body is provided at least on the low-pressure side of the step, and 
 an annular groove formed in the outer circumferential surface of the rotating body to circumferentially extend and to be located in at least a portion of an area between the step and the fin that is provided close to the low-pressure side compared to the step, 
 wherein the annular groove has a low-pressure-side side surface and a high-pressure-side side surface where the high-pressure-side side surface is flush with the annular surface of the step. 
 
     
     
       2. The labyrinth seal according to  claim 1 , wherein a distal end of the fin that is provided close to the low-pressure side compared to the step is located close to the high-pressure side compared to a proximal end of the fin. 
     
     
       3. The labyrinth seal according to  claim 1 , wherein an outline of the annular groove has an arc shape in a cross-section including the axis of rotation. 
     
     
       4. The labyrinth seal according to  claim 2 , wherein an outline of the annular groove has an arc shape in a cross-section including the axis of rotation. 
     
     
       5. The labyrinth seal according to  claim 1 , wherein in a cross-section including the axis of rotation, a low-pressure-side side surface of the annular groove has such a shape that a radially inner end thereof is located close to the high-pressure side compared to a radially outer end thereof. 
     
     
       6. The labyrinth seal according to  claim 2 , wherein in a cross-section including the axis of rotation, a low-pressure-side side surface of the annular groove has such a shape that a radially inner end thereof is located close to the high-pressure side compared to a radially outer end thereof. 
     
     
       7. The labyrinth seal according to  claim 1 , wherein the annular groove is formed to extend axially from a position of the step toward the low-pressure side. 
     
     
       8. The labyrinth seal according to  claim 7 , wherein when an axial distance between the step and a distal end of a low-pressure-side surface of the fin that is provided close to the low-pressure side compared to the step is defined as G and an axial opening width of the annular groove is defined as W, 0.78<G/W<1.22 is satisfied. 
     
     
       9. The labyrinth seal according to  claim 1 , wherein a plurality of the steps is formed on the outer circumferential surface of the rotating body such that the diameter of the rotating body gradually decreases from the high- pressure side toward the low-pressure side, and the fin is provided at least close to the low-pressure side compared to each of the steps. 
     
     
       10. The labyrinth seal according to  claim 2 , wherein the annular groove is formed to extend axially from a position of the step toward the low-pressure side. 
     
     
       11. The labyrinth seal according to  claim 3 , wherein the annular groove is formed to extend axially from a position of the step toward the low-pressure side. 
     
     
       12. The labyrinth seal according to  claim 4 , wherein the annular groove is formed to extend axially from a position of the step toward the low-pressure side. 
     
     
       13. The labyrinth seal according to  claim 5 , wherein the annular groove is formed to extend axially from a position of the step toward the low-pressure side. 
     
     
       14. The labyrinth seal according to  claim 6 , wherein the annular groove is formed to extend axially from a position of the step toward the low-pressure side. 
     
     
       15. The labyrinth seal according to  claim 1 , wherein an annular groove has a high-pressure-side surface and a low-pressure-side side surface formed on the outer circumferential surface of the rotating body, and
 wherein an axial position of a distal end of the fin is substantially same as an axial position of the low-pressure-side side surface of the annular groove.